Electrically controlled braking or accelerating apparatus

ABSTRACT

An electrical analogue signal-controlled, vehicle braking control apparatus includes a dynamic braking arrangement responsive to an electrical command analogue signal corresponding to the braking force desired and a summing circuit which operates during braking in response to a command analogue signal and a signal corresponding to the actual braking produced, to produce an electrical signal used in controlling an additional braking arrangement so that any deficiency in the dynamic braking called for by the command analogue signal is compensated for.

United States Patent [ll] E Maskery Reissued Sept. 2, 1975 ELECTRICALLYCONTROLLED BRAKING [56] References Cited OR ACCELERATING APPARATUSUNITED STATES PATENTS [75] Inventor: Ar hur Mask ry, L n n. E g n3,398,815 8/1968 Brath et a1. 303 22 R x [73] Assignee: WestinghouseBrake & Signal C0., 2:2 at London, England [22] Filed: Sept. 18, 1972Primary Examiner-Trygve M. Blix I Assistant ExaminerStephen G. Kunin[21] Appl' 289846 Attorney, Agent, or FirmLarson, Taylor and HindsRelated US. Patent Documents Reissue Of; 57 ABSTRACT [64] Patent 3547499An electrical analo ue si al-controlled, vehicle brakl d D 15 1970 g iing control apparatus includes a dynamic braking ari A 19 1968 rangementresponsive to an electrical command analc logue signal corresponding tothe braking force desired and a summing circuit which operates during[30] Forelgn Apphcanon Priority Data braking in response to a commandanalogue signal and P 1967 United Kingdom [9234/67 a signalcorresponding to the actual braking produced, 4 to produce an electricalsignal used in controlling an 303/22 R additional braking arrangement sothat any deficiency [5l Int. Cl 136% 8/18 in the dynamic braking calledfor by the command [58] Field of Search 303/3, 20, 21 A, 22 R; alogucsignal is compensated 28 Claims, 8 Drawing Figures 3 JERk CMITRJl UNIT 5I RING PHASE Holman] AMHl/ZW sffijlf/yf I 0 L e! RECT/f/[R l 2 i l ll 1llVPl/T I J 6 Ac. SIGNAL F/XFD 8M5 SIGNAL I4- l5 [l6 3 V 7a i LOADSUMMING CIRCUIT $I6NAL E- I? BRAKE Reissued Sept. 2, 1975 7 Sheets-Sheet2 COMMAND 24 2| SUPPL Y 2 5 ZERO RFRENCE 7 Sheets-Sheet 5 PRESSURETRANSDUCER Fig. 2b.

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Reissued Sept. 2, 1915 Re. 28,538

'7 Sheets-Sheet 5 SUPPLY In army/c j-jvq alum/a HEM/.5 1 S/GIVAL CURRENTOUTPUT ELECTRICALLY CONTROLLED BRAKING ()R ACCELERATING APPARATUS Matterenclosed in heavy brackets I: appears in the original patent but formsno part of this reissue specification; matter printed in italicsindicates the additions made by reissue.

This invention relates to electrically controlled braking oraccelerating apparatus and relates especially to apparatus which isresponsive to an electrical analogue signal.

According to the present invention there is provided an electricanalogue signal controlled vehicle braking control apparatus includingdynamic braking means responsive to an electric command analogue signalindicative of a desired braking effort and summing means operable duringbraking to be responsive to the command analogue signal and anelectrical signal indicative of the degree of dynamic braking producedto provide an electrical signal for controlling additional braking meansto tend to make up any deficiency in the dynamic braking as called forby the command analogue signal.

The invention further provides electric analogue signal controlledvehicle braking control apparatus in cluding means responsive to anelectric command analogue signal indicative of a desired braking effort,means for applying a variable signal dependent thereon to a vehicleweight responsive amplifier to produce a weight dependent electricsignal for addition to said variable signal to produce a load-weightedelectrical signal for dynamic braking control means and summing meansoperable during braking to be responsive to the command analogue signalthe weight dependent signal and an electrical signal indicative of thedegree of dynamic braking to produce an electrical signal forcontrolling additional braking means to tend to make up any deficiencyin the dynamic braking as called for by the sum of the weight dependentsignal and the command analogue signal.

It is a feature of the invention that the loadwcighted signal can have aparameter which is variable according to the value of the commandanalogue signal said parameter being indicative of whether the magnitudeof the command analogue signal represents a degree of braking or adegree of traction and the apparatus may include means responsive tosaid parameter to condition the apparatus to provide dynamic brake ortraction in accordance with the load weighted signal.

The said parameter may be a phase relationship relative to a referenceAC. signal and said means responsive to said parameter may be a phasesensitive rectifier.

The weight responsive amplifier preferably includes a pressuretransducer to which fluid pressure from a load sensing means of thevehicle is applied to vary the magnitude of the variable signal toproduce the weight dependent signal.

Further, electrical means is preferably provided when the additionalbraking means is electropneumatically associated with said summing meansfor, when the variable signal is indicative of a braking mode. applyinga predetermined bias thereto such as to impose a restricted brakeapplication by the additional braking means.

In addition, a coast region may be allocated to said command analoguesignal between ranges thereof corresponding to a braking mode andcorresponding to a traction mode.

Further, apparatus in accordance with the invention preferably embodiesmeans for preventing more than an acceptable rate of change of theanalogue signal. This is especially valuable to provide jerk control inapparatus for controlling braking and traction of rail vehicles toreduce mechanical stressing or passenger discomfort.

The present invention is especially but not exclusively applicable toequipment employing apparatus such as described in the U.S. Pat.application Ser. No. 600,799, now abandoned.

In order that the present invention may be more clearly understood andreadily carried into effect the same will be further described by way ofexample with reference to the accompanying drawings in which:

FIG. 1 is a block diagram illustrative of the basic principles involvedin the present invention,

FIGS. 2a, 2b and 2c when placed together illustrate in greater detail acircuit arrangement for a loadcontrolled amplifier and related circuitsfor the equipment associated with one rail vehicle bogie,

FIG. 3 illustrates a summing circuit and constant current ampliler foreleetropneumatic brake control in response to signals provided by theremaining circuits,

FlGS. 4a and 4b placed together illustrate details of ajerk controlcircuit to be referred to hereafter and FIG. 5 illustrates a pressuretransducer also to be referred to.

Before discussion of the specific embodiment of the invention to bedescribed herein, it is to be understood that the present embodiment isa braking and traction control system operating in response to themagnitude of an applied DC. current analogue signal and the apparatus issuitable for controlling the motored and braked axles of a train havinga number of interconnected cars. A DC. command analogue signal isderived from a drivers control unit which forms no part of the presentinvention as such and is fed to each of the cars in series over a pairof conductors passing the full length of the train. It is preferably toemploy a current analogue signal, as opposed to a voltage analoguesignal, for the reason that it is possible to provide a constant currentsupply for the analogue signal but if one used a voltage anlogue signalit would necessitate compensation for variation of overall voltage dropwhich occurs when a change in the number of cars in a train is effected.

It is also to be understood that the present system is arranged not onlyto control the electro-pneumatic braking facilities of the train and thetraction facilities provided thereon but also to control dynamicbraking, a deficiency in the dynamic braking being made up for by theelectro-pneumatic braking.

Further, it will be appreciated that it is desirable to control thetractive effort applied to any given car by the motors on the respectivebogics thereof and also in converse, the braking effective on thosebogies, in accordance with the loading of the bogies. Accordingly. foreach end of a car, load weighing equipment is as sumed to be providedand this provides a fluid pressure dependent upon vehicle loading to apressure transducer which modifies the degree of acceleration or thedegree of braking individually for the individual bogies of cars in atrain. Thus, it will be appreciated that while a particular currentanalogue signal is applied from the driver control equipment to all thecars on the train, the equipment associated with each bogie of each carmodifies the response of the braking apparatus or traction apparatus inaccordance with the loading experience thereat.

It is an important outcome of equipment in accordance with the presentembodiment of the invention that in the unlikely event of failure of theload weighing equipment on a car or of electronic circuits associatedtherewith, the electro-pneumatic braking remains uneffected by virtue ofthe fact that the command analogue signal before application to theamplifier which includes the pressure transducer, is applied right roundthe whole of the equipment to the summing means so as to provide atleast braking effort up to a set tare weight level.

Referring to FIG. 1, of the drawings, the terminals 1 and 2 are theinput terminals for receiving a control DC. current analogue signal andthese are connected to a so-called jerk control unit represented by theblock 3. This jerk control unit may be of a form to be described ingreater detail hereafter with reference to FIG. 4, and is provided forensuring that the command analogue signal cannot change at more than apredetermined acceptable rate regardless of the rate of change of thesignal which is applied to the terminals 1 and 2. This is desirable forthe two-fold reasons that firstly the braking must never be allowed tobe so excessive as to cause substantial discomfort to passengers in atrain and secondly, the currents applied to traction motors must also belimited such as to not command the motors to provide more than apredetermined degree of acceleration. Such excessive acceleration cancause not only discomfort to the passengers but over-loading of thetraction motors and consequently highly expensive damage to the tractionequipment. The output of the jerk control unit 3 is a DC. analoguesignal and in the present example is assumed to vary between and 10volts, the range 0 to approximately 5 volts corresponding to the brakingrange of control and the range from approximately 5 volts to voltscorresponding to the traction range of control. It will be understoodhere that maximum traction is attained at a value of the commandanalogue signal of 10 volts and maximum braking is attained at a valueof the command analogue signal of approximately zero volts. The commandanalogue signal is applied to a so-called ring modulator 4, to a secondinput 5 of which there is also applied a five volt reference signal thepurpose of which will become apparent hereafter. The ring modulator alsoreceives a basic carrier frequency of 25 kc. s from a multivibratoroscillator represented by the block 6. The variable signal output of thering modulator consists of an AC. the magnitude of which is dependentupon the degree of braking or acceleration called for by the commandsignal and the phase of which is dependent upon whether the signalrepresents braking or acceleration. This signal is applied to anamplifier 7 to which a load signal is applied at 7a such that theamplifier produces a weight dependent output signal and this signal isapplied to an adding circuit represented by the block 8 to which theoutput of the ring modulator 4 is additionally applied. The combinationof the amplifier 7 and the adding circuit 8 may be regarded as amultiplication circuit. The signal applied from the output of themodulator 4 to the adding circuit 8 can be regarded as the controlsignal for purely tare weight on the bogie in question and the amplifieroutput may be regarded as the extent to which this signal requires to besupplemented for added loading on the vehicle. The output of the addingcircuit 8 is therefore an A.C. signal proportional to the requireddegree of braking or the required degree of acceleration for the portionof the train under consideration and this is, therefore, termed the loadweighted signal. The phase of this signal is the parameter thereofdetection of which determines whether the signal is a braking controlsignal or an acceleration control signal and this is determined by thephase sensitive rectifier 9 which has an output applied to it from theoscillator 6 and which determines whether the output should be on theline 10 for feeding to the dynamic braking control apparatus or to theline 11 for feeding to the traction control apparatus of the particularbogie of the car in question.

A summing circuit represented by the block 12 is provided the output ofwhich controls the electropneumatic braking equipment of the particularbogie on the car in question and this receives a signal on the line 13which is a DC. signal proportional to the command analogue signal, asignal on the line 14 which is a rectified signal proportional to theload responsive signal received from the amplifier 7. A further signalis applied to the line 15 and this is a signal derived from the dynamicbraking part of the control equipment and which is not described hereinbut is a DC signal indicative of the degree of dynamic braking beingproduced. A further bias signal is applied to the line 16 to provide asreferred to later, a basic restricted application of theelectro-pneumatic brake for reasons which are well known in that it isalways necessary to take up the slack etc. in the braking equipmentbefore the brakes are actually effective. The summing circuit 12therefore is arranged to be operative to blend the electro-pneumaticbraking with the dynamic braking to provide the desired degree ofbraking in accordance with the sum of the signals appearing on lines 13and 14.

It will be seen from the foregoing that in the event of the portions ofthe circuit consisting of blocks 7, 8 or 9 failing, the circuit 12continues to receive a control signal in the form of the signal on line13 and therefore the electro-pneumatic braking is effective to producebraking at least to the tare weight value.

Whilst the apparatus shown in FIG. 1 is intended to be present on eachmotored and braked car of a train to which the system is applied, theapparatus to the right of the ring modulator is required to beduplicated for each bogie ofa car which is to be controlled. In theinterests of simplicity, only apparatus appropriate to a single bogiehas however been shown.

Referring now to FIGS. 2a, 2b, 2c and 3 which when placed togetherillustrate in greater detail the circuit arrangement which is shown inblock form in FIG. 1., the circuit has two supply lines 21 and 22 whichcarry respectively the 5 volt reference which has already been mentionedand a positive supply of approximately 15 volts for the circuit, a zeroreference being connected at terminal 23. The input command analoguevoltage signal which is derived from the jerk control circuit which isnow shown, is applied to the terminal 24.

Considering first the oscillator circuit, this consists essentially oftwo transistors of the n-p-n type represented by reference and 26 thesetransistors have their emitters connected via a diode 27 which providesa slight bias in the of condition of transistors 25 or 26 to the zeroreference line 23 and their bases are also connected to this line viarespective resistors 28 and 29. The collector electrode of transistor 26is crosscoupled via a resistor 30A a capacitor 28 and a diode 32A to thebase electrode of transistor 25 and similarly the collector electrode oftransistor 25 is cross-coupled via a resistor 30, a capacitor 31 and adiode 32 to the base electrode of transistor 26. The anodes of thediodes 32A and 32 are connected via respective resistors 33 and 34 tothe positive supply line which is connected to the terminal 22. Further,the junctions of 33 and 34 are connected to a centre tapping on theprimary winding of a transformer indicated generally by the reference 35the outer terminals on which primary windings are connected to thecollector electrodes of 25 and 26 as shown. The transistors 25 and 26thus cross-coupled in such a manner and operate between the supply lines22 and 23 as to provide a fixed voltage A.C. signal on the primary oftransformer 35 this signal being adjusted to approximately 2.5 kc.s.

The transformer 35 has a centre tapped secondary winding, the centre tapof which is connected to the command analogue signal input line 24 andthe terminals of this winding are connected on the one hand via a diode36, resistors 37 and 38 and a diode 39 and on the other hand via a diode40, resistors 41 and 42 and a further diode 43. The connections if thelast pair of diodes and 43 are oppositely poled to the connections ofthe previous pair of diodes 36 and 39 with re spect to the secondarywinding of the tranformer 35 and the junctions of resistors 37 and 38and 41 and 42 respectively are connected to opposite ends ofa centretapped primary winding 44 of a further tranformer 45. The lattertransformer has two secondary windings 46 and 47 as shown. As will beseen hereafter, the components associated with the secondary winding oftransformer 35 and the primary winding of tranformer 44 operate toprovide a ring modulator as previously referred to with reference toFIG. 1.

The secondary winding 47 of the tranformer is connected on the one handvia a resistor 48 to the zero line for the circuit and on the other handto the base electrode of an amplifier transistor stage embodying thetransistor 49 which has collector and emitter resistors 50 and 51respectively. The collector electrode of transistor 49 is furtherconnected to the base electrode of another transistor stage 52, theemitter electrode of which is connected via a Zener diode 53 and aresistor 54 to the zero reference line, thejunction of 53 and 54 beingconnected to the base electrode of yet another transistor 55. Thecollector electrode of transistor 55 is connected via the primarywinding of a transformer 56 to a 40 volt supply line at the point 57 asindicated and the emitter electrode of transistor 55 is connected via anemitter resistor 58 to the zero reference line. A resistance capacitancecoupling via capacitor 59 and resistor 60 is made between thecollector-electrode of 55 and the emitter electrode of transistor 49 asshown and further negative feedback path to stabilise the working pointof the amplifier embodying transistors 49, 52 and 55 is provided via aresistor 61 to thejunction of 45 and 48 as shown. The purposes of thefeedback coupling from the collector electrode of transistor 55 is toprovide A.C. feedback for the purposes of stabilising the gain of theamplifier.

The transformer 56 has a centre tapped secondary winding 63 the mainterminals of which are connected to a suitable electromagnetic pressuretransducer represented by the block 64 and described in greater detailhereafter with reference to FIG. 5. The transformer 56 also has twofurther secondary windings 65 and 66 which provide A.C. output signalsfor addition to the weight responsive signal for the purposes ofproviding a load weighed signal for controlling the dynamic brak ing ofthe traction of the car in question as will be described hereafter. Thecentre tape of the secondary winding 63 is connected via a resistor 67to the zero reference line to provide a reference for this transformerand the output of the pressure transducer 64 is applied to the baseelectrode of a further transistor amplifier stage 68, the collectorelectrode of which is connected to the terminal 22 via a resistor 69 andthe emitter of which is connected to the zero reference line via aresistor 70. The collector electrode of transistor 68 is furtherconnected to the base electrode of another transistor stage of thisamplifier and the transistor 71 the collector electrode of which isconnected to the terminal 22 and the emitter electrode of which isconnected via a diode 72 and a resistor 73 to the zero reference linevia a resistor 75 across which there is connected a biassing capacitor76. The collector electrode moreover of transistor 74 is connected tothe aforementioned 40 volt supply line at terminal 76 via the primarywinding 77 of yet another transformer 78. The gain of the amplifiercomprising transistors 68, 71 and 74 is stabilised via a negativefeedback path including capacitor 79 and resistor 80 from the collectorelectrode of transistor 74 to the emitter electrode of transistor 68.Further, the working point of the amplifier is stabilised by a DC.connection between the emitter electrode of transistor 74 via resistor81 to the centre tap of the secondary winding 63 of transformer 56.

As will be seen hereafter the signal developed in the primary winding 77of transformer 78 is the weight responsive signal and the transformer 78has a centre tapped secondary winding 82 which is included in a centretapped rectifier arrangement embodying the rectifiers 83 and 84 asshown. The junction of the cathodes of 83 and 84 being connectedtogether to provide an output which is one signal to be fed to thesumming circuit.

The upper terminal of the secondary winding 83 is further connected viathe aforementioned additional secondary winding 65 of the transformer 56to a further diode 85 and similarly the lower terminal of the winding 82is connected via the secondary winding 66 of 56 to another diode 86. Thelatter diodes co-operate respectively with pairs of transistors 87 and88 and 89 and 90 to form phase sensitive rectifier arrangements fordiscriminating between A.C. signals indicative of required braking bydynamic braking and signals indicative of required traction. For thispurpose, the cathode of diode 85 is connected to the collector-electrodeof transistor 87 and also to the collector electrode of transistor 90.The emitter electrode of transistor 87 is connected in common with theemitter electrode of transistor 88 the collector electrode of which isconnected to the cathode 86. Similarly, the base electrodes of the pairof transistors 87 and 88 are coupled together via a resistor 91 and anauxiliary secondary winding on the transformer 35 which, therefore,receives the basic oscillator frequency and phase. The emitter electrodeof 87 is further connected to the base thereof via a diode 92 and asimilar diode 93 is provided for transistor 88. Diodes 92 and 93 providereturn paths for the base current of whatever transistor is on andthereby enables the two transistors 87 and 88 to be driven from onewinding 97. Referring now to the other pair of transistors 89 and 90,these have bases and emitters connected via respective diodes 94 and 95as shown and their bases are connected together via a resistor 96 and afurther auxiliary secondary winding 98 on the transformer 35 to receivealso the basic oscillator frequency. The output from the phase sensitiverectifier corresponding to a load weighted dynamic braking signalappears on the line 99 and the output of the phase sensi tive rectifiercorresponding to a load weighted traction signal appears on the line 100the signal appearing on the line 101 is as aforementioned, the loadresponsive signal for application to the summing circuit for controllingthe electro-pneumatic braking for blending with the dynamic brake. Thesumming circuit will be described in greater detail hereafter.

Referring now to the operation of the circuit arrangement as describedso far, it will be appreciated that the apparatus as described is as forcontrol of one bogie of a car of a train and the part of the apparatuswhich is coupled to the transformer winding 47 of transformer 45 is inpractice duplicated and coupled to the transformer winding 46 forproviding load-weighed control of braking and traction for the otherbogieof the car of the train.

As aforementioned, the multi-vibrator formed around the transistors 25and 26 produces a 2%: kc. A.C. signal which is applied over thetransformer 35 to the secondary winding thereof incorporated in the ringmodulator. It will be recalled moreover that the centre tapping of thewinding 44 of transformer 45 is connected to the 5 volt reference sourcefor the circuit. Further, by noting the polarity of the diodes 36 and 39it will be appreciated that when the upper end of the secondary windin gof 35 is positive relative to the lower end, the junction of equalresistors 37 and 38 acquires the potential of the centre tapping of 35namely the command analogue signal voltage applied from the terminal 24.Depending therefore upon which way the command analogue voltage deviatesfrom 5 volts, the potential of the centre tapping 44, so the phase ofthe variable A.C. signal in the windings 46 and 47 is either at or 180phase relationship to the output of the oscillator. Further, themagnitude of the voltage induced across windings 46 and 47 isproportional to the deviation from volts of the command analogue signal.

Considering now the secondary winding 47, being that corresponding tothe circiut for the bogie in question, the voltage induced in thiswinding is amplified via the transistor stages 49, 52 and 55 andprovides an alternating current proportional thereto in the primarywinding 57 of transformer 56 which produces an A.C. signal to thepressure transducer 64. The pressure transducer 64 is adjusted such thatfor normal tare weight loading on the bogie in question there issubstantially no output to the amplifier, the first stage of which is 68but as the loading of the vehicle is increased so the output signal 68increases proportionately. The output of the pressure transducertherefore and the weight dependent signal may be regarded as the signalsupplementation for the normal weight on the vehicle by loading thevehicle by passengers or otherwise. This signal is then amplified andproduces an A.C. signal in the primary Winding 77 of the transformer 78to produce a corresponding A.C. voltage across the secondary winding 82.This signal is then rectified via diodes 83 and 84 to produce a weightresponsive signal in the line 101 which is connected to the summingcircuit yet to be described.

Considering now the transistors 87 and 88, these transistors receive abase drive from one of the aforementioned auxiliary windings on thetransformer 35 in accordance with the basic oscillator phase andfrequency and therefore the transistors 87 and 88 receive a base drivealternately at the basic frequency. Further, it will be recalled thatthe diode 85 is forward biassed on appropriate half cycles of the signalreceived from the transformer and from the transformer 78. Accordingly,only when the phase relationship between the signals received from thetransformer 35 and the transformer 56 are in appropriate phaserelationship is to be determined does the current through the rectifierpass through the transistor 87 to provide the corresponding half cycleof a dynamic braking signal on the line 99. Similarly, only when thesame conditions exist, does the other half cycle pass via the receifier86 and the transistor 88 to the line 99. When the phase relationshipbetween the signals in transformers 56 and 78 and the transformer 35 isthe opposite to the previously described relationship, the transistors89 and 90 are operative respectively to conduct the respective halfcycles via the rectifiers 86 and 85 to provide an acceleration ortraction signal in the line 100. Dependant therefore on the phaserelationship between the load responsive signal and the basic oscillatorfrequency a signal is produced in the output lead 99 or 100. Sincemoreover the signal induced in the winding 65 or 66 is proportional inmagnitude to the unload-weighted command analogue voltage signal derivedfrom the terminal 24, the output derived at the line 99 or 100 isproportional to the sum of this signal and the load responsive signalinduced in the winding 82. The transformation ratios of the transformersof course, are suitably selected to achieve this end. The outputsappearing on line 99, 100

and 101 are in practice applied to buffer amplifiers but these may be ofsuitable form and will not be described in detail herein. The outputs ofthese amplifiers are then utilised for control purposes and the outputsof 99 and 100 after amplification in the buffer amplifiers are appliedto the summing circuit in which blending of the dynamic and BF. brakingis achieved.

Referring now to the summing circuit, this is illustrated in greaterdetail in FIG. 3 of the drawings. The summing circuit consists basicallyof a transductor having a pair of A.C. windings 102 and 103 connected toreceive an A.C. supply from a suitable inverter which is not shown butwhich is connected to terminals 104 and 105 as shown. The transductorhas the opposite ends of the windings 102 and 103 connected together viarespective rectifiers 106 and 107 and the transductor has five D.Cvcontrol windings 108 and 112 as shown. The command analogue voltagesignal at the terminal 24 previously mentioned is connected via aresistor 113 to the control winding 108 of the transductor and the loadresponsive signal derived from the line 99 previously referred to isapplied to the winding 109 of the transductor via a terminal 114 and aresistor 115. The winding 110 of the transductor is connected via aresistor 116 to terminals 117 and 118-to receive a signal from thedynamic braking means of the particular bogie of the train in question,indicative of the degree of dynamic braking being produced at anyinstant of time. Further, a bias is applied to the transductor via thecontrol winding 111 from the terminals 119 and 120 which are at -24volts and +15 volts respectively.

' The final control winding of the transductor namely,

112 is arranged via a resistor 121 to receive a set degree of DC.feedback from the output of the circuit to achieve stability ofoperation.

In addition to the aforementioned fixed bias applied to the bias winding111 of the transductor a further bias is applicable via a resistor 123and the collector emitter path of a transistor 124. Componentsassociated with this transistor are resistor 125, diodes 126 and 127 andresistors 128 and 129 connected as shown. The terminals to whichresistors 128 and 129 are connected, namely, terminals 130 and 131, areat+ volts and 12 volts respectively.

In operation of the summing circuit the transductor and associatedcomponents are so adjusted that the basic command analogue signal at thecoast level that is the level which neither calls for braking nortraction, namely, 5 volts, gives rise to a transductor output voltage inconjunction with the bias derived via the resistor 133, of 6 volts.However, the additional bias imposed by the conducting condition of thetransistor 124 increases this output to 8 volts in the coastingcondition for the equipment. As the magnitude of the voltage analoguesignal at the terminal 24 reduces to command a braking application thatis it reduces from 5 volts towards the zero level, the output from thecircuit on line 132 begins to fall and when the signal at 24 reachesapproximately 4.6 volts, the transistor 124 becomes non-conducting andremoves some of the bias from the winding 11 1 thereby reducing theoutput to provide immediately a restricted application which takes upthe slack in the electropneumatic brake mechanism at an output ofapproximately 6 volts on the line 132. From then onwards towards thezero voltage level for the signal at the terminal 24, the output voltageon the line 132 reduces steadily towards the full electropneumatic brakeapplication condition.

Considering the extreme case now where the dynamic brake is providingthe full demanded braking effort that is the input on the DC. winding110 on the transductor balances the combined signals on the windings 108and 109, the signals exactly match and the voltage on the output line132 remains at the restricted application level of 6 volts.

Considering now the other extreme case where there is no dynamic brakeapplication and considering that the signal at the terminal 24 movesfrom the 5 volt level, one passes through the restricted applicationregion at which the output on the output line 132 is 6 volts and theregion 5 volts to 4.6 volts input at 24 provides a minimum coasting areaof control for the driver. The output derived on the line 132 is thenproportional to the sum of the ampere turns of the windings 108 and 109on the transductor and the output on line 132 falls towards the maximumbraking level as the voltage at terminal 24 reduces still further.

As mentioned previously, if the load responsive signal which energisesthe winding 109 fails, one is left with the variable signal on thewinding 108 corresponding to the unload weighted command analogue signaland, therefore even in the event of failure of the load weighing part ofthe circuit, the light-loaded braking component still remains to give anelectro-pneumatic braking application.

It will be recalled that apparatus in accordance with the presentinvention may be employed in conjunction with braking apparatus such asdescribed in co-pending patent application Ser. No. 600,799. In theevent of an electropneumatic converter of the type described in thatspecification being empolyed, it may be desirable to ensure that theampere turns of the converter are substantially independent of thetemperature coefficient of impedance presented by the coil of theconverter. Accordingly, the output appearing on the line 132 of thesumming circuit just described is applied to a constant currentamplifier circuit based on a further transductor 140.

The transductor has a construction similar to that of the summingcircuit, having two A.C. windings and 146 and four DC. control windings147, 148, 149 and 150. The winding 147 provides load current negativefeedback; winding 148 has a 15 volt bias source connected to it via aresistor 151 to set the working point for the amplifier; winding 149receives the input signal from line 132 and winding 150 is con nected asa negative feedback winding taking its voltage across the resistor 156.The latter feedback path is via a zener diode and is operative duringbraking but provides current limiting during traction. The currentoutput of the circuit is derived via the filter comprising inductance152 and capacitor 153 from the line 156. The resistor 157 moreover,being returned to the minus 12 volt terminal 131, introduces a negativecurrent corresponding to the magnetization current of the transducerinto the output in order that the current as applied to the convertermay be reduced to zero. The filter provides smoothed DC. output.

Considering this constant current amplifier in slightly more detail, thesignal applied to the line 24 of the summing circuit rises to say +10volts during an acceleration and the output on the line 132 may rise tosome thing more than 8 volts and calling for a current in theelectro-pneumatic converter in excess of that which is required to turnit off. In order to avoid overheating in the converter coil, thiscurrent is preferably restricted to about 600 ma. The resistor 156 whosevalue may be about 12.5 ohms and which is in series with the convertercoil, has a voltage across it proportional to the converter current andprovides feedback via winding 150 as referred to above. Diodes 155 and158 start to conduct at approximately 7.4 volts corresponding to 590 ma.of converter current, the diode current passes through winding 150 whichis arranged to give additional negative feedback to tend to limit theoutput current.

Considering now the greater detail of the jerk control block 3 of FIG.1, and referring to the drawing of FIG. 4 an input D.C. analogue signalfrom the drivers control unit is applied to the terminals 201 and 202,these terminals being connected to a DC. control winding 203 on atransductor represented by the general reference 204. The transductor204 also has two further D.C. biassing windings 205 and 206 as shown andthese will be referred to hereinafter. The AC. windings of thetransductor 204 are connected to input terminals 207 and 208 to which analternating current supply in the present example 224 volts, 400 cyclesper second, is connected. The output side of the transductor mainwindings are connected to rectifiers 209 and 210 as shown to provide adirect current output via a resistor 211 to an arrangement of diodesrepresented by the general reference 212. A zero DC. voltage referencefor the circuit is connected to the terminal 213 and the circuit is alsoprovided with supply voltages of minus 24 volts and plus 24 volts at theterminals 214 and 215 as shown and plus 15 volts and minus 12 volts atthe ter" minals 216 and 217. A pair of resistors 218 and 219 areconnected between the outputs of diodes 209 and 210 and the zero voltsline for the circuit and a feedback resistor 220 is connected betweenthe latter output and one terminal of the further winding 206 on thetransductor the other terminal of this winding being con nected to thezero volts line. Between the output side of the resistor 211 and thezero volts line there is connected a capacitor 221 of relatively lowvalue and also between this output and the minus 12 volts line a furtherresistor 222 is connected.

The arrangement of diodes 212 consists of four diodes 223, 224, 225 and226 respectively arranged in a bridge configuration, the diodes 223 and224 being back-to-back and the diodes 225 and 226 being backto-back suchthat assuming all the diodes are biassed to conduct, a series DC currentpath is provided from the terminal 214 via a resistor 227, transistor228, transistor 229 of opposite type to 228 and a further resistor 230to the minus 12 volts line connected to the terminal 217. The conditionsof the transistors 228 and 229 are determined by Zenor diodes 231 and232 connected in their base emitter paths, these diodes being connectedin a series path including a further resistor 233 between the linesconnected to terminals 214 and 217 respectively. The junction of diodes224 and 226 is connected to one terminal of a storage device in the formof a relatively large capacitor 233a, the other terminal of which isconnected to the zero volts line for the circuitv Further, the capacitor233a has connections to an output amplifier circuit represented by theblock 234. One output of the amplifier consists of a continuation of thezero volts line to output terminal 235 and the other output terminal,the output of which varies in accordance with the input to the circuit,is represented by 236 and has a feedback connection via a resistor 237also to the further winding 206 of the transductor referred topreviously. The amplifier 234 may be of any suitable form providing astable output in response to the input signal voltage across thecapacitor 233a and in view of the fact that feedback is taken from theoutput of the amplifier, it is necessary to sup ply the amplifier fromthe supply lines to the remaining part of the circuit and connectionsare, therefore, shown from the terminals 216 and 217 for this purpose.In addition, in order that the transductor 204 may have a predeterminedoperating point, that is, it may be adjusted such, for example, to givea zero output for a zero input, the further biassing winding 205 isconnected via respective resistors 238 and 239 to the supply voltages atterminals 215 and 216 as shown, to provide a reference bias on thetransductor.

in operation of the circuit arrangement shown in the drawing of FIG. 5the direct current analogue signal is applied to the winding 205 of thetransductor and thereby influences the magnitude of the alternatingcurrent to which the transductor can be responsive and the output of thetransductor being supplied via diodes 209 and 210 becomes a directcurrent voltage across the capacitor 221 and is applied to the junctionof diodes 223 and 225 of the diode arrangement 212. Assuming initiallythat the voltage across the relatively low capacitor 221 and therelatively high value capacitor 233a are the same, the diodes 223, 224,225 and 226 are biassed into the conducting condition and carry theemitter collector current for the transistors 228 and 229 between thesupply lines connected to terminals 214 and 217. In the event ofa suddenrise in the analogue signal applied to the transductor 204, the outputof the transductor increases proportionately and produces aproportionate increase of voltage on the capacitor 221. Since there isno instantaneous change of voltage across the capacitor 23321, the diode223a becomes biassed into the non-conducting condition and current flowsvia the collector emitter path of the transistor 228 into the capacitor233a until the voltage on the capacitor 233a has attained a value whichis substantially equal to the voltage from the capacitor 221. Duringthis current flow the diode 226 is similarly biassed to the diode 223and in view of this it is nonconducting whereas the diode 225 is biassedinto the conducting condition. Since, however, the emitter conductoroutput impedance of the transistor 229 via the resistor 230, which is ofsubstantially high value compared with the resistor 211, virtually noappreciable current flows into the transistor 229 from the capacitor221.

Taking now a condition under which a sudden reduction in voltage occurs,across the capacitor 221 due to a sudden reduction in the DC. currentanalogue signal applied to the winding 203 of the transductor, if thischange takes the voltage of the capacitor 221 below that of therelatively large capacitor 233a, the diode 225 is now biassed into thenon-conducting condition and carries current via the transistor 229 tothe capacitor 233a. From the point of view of the capacitor 233a, thiscurrent is of opposite sense to the current flow which took placepreviously as described above via the diode 224 and, therefore, areduction of voltage across the capacitor 233a takes place until thepoint is reached at which the voltages across the capacitors 221 and233a are again substantially equal.

Since the transistor 228 and 229 have mixed control potentials appliedto them, the control of the emitter collector paths being across theZener diodes 231 and 232, these transistors operate as constant currentdevices and therefore, the paths via which the capacitors 233a ischarged or discharged in accordance with the sense of variation of thevoltage across the capacitor 221, are constant current circuits. Thecircuit values may, therefore, be chosen such that whatever the rate ofchange of the analogue signal applied to the terminals 201 and 202 ofthe circuit, the voltage across the capacitor 233a changes at apredetermined rate.

Clearly, in the foregoing, the forward voltage drops which are presentduring the conduction of the diodes 224 or 226 as discussed in theforegoing have been ignored and it will be appreciated that if thecircuit val ues are appropriately chosen, these forward voltages canonly give rise to an insignificant discrepancy be tween the values ofthe voltages developed across the capacitors 221 and 233a in a restcondition for the circuit.

The feedback path from the terminal 236 to the winding 206 of thetransductor provides for increased stability of the circuit and alsostability of the transductor itself is achieved by the addition offeedback via the resistor 220.

Referring in greater detail to the transducer of block 64 of FIG. 2b,and as shown in FIG. 5, the transducer of FIG. 5 comprises an outercasing made up of two sections 301 and 302. The section 1 contains themain electrical component of the transducer and the section 302 is inthe form of an air-tight chamber having an input port 303 connected toreceive pressure according to vehicle bogie loading via which fluidpressure can be applied to the upper surface of a pressure responsivemember 304. The pressure responsive member 304 is sealed into the deviceby means of a diaphragm 305 which is clamped between 301 and 302. Thesection 302 is also provided with a threaded member 306 which can bescrewed into or out of 302 from the outside if desired to exert adesired force independently of the pressure at 303 on the pressureresponsive member 304. With no pressure exerted by 306, pressureresponsive member 304 is balanced between two substantially equalsprings 307 and 308 in the upper and lower parts of the device so thatmovement of 304 is substantially linear with increase of pressure in theupper enclosure, the lower enclosure being assumed to be at atmosphericpressure. The springs 307 and 308 are preloaded on assembly by an amountgreater than the maximum stroke under pressure of the pressureresponsive member 304, so that at full stroke both springs are still ina compressed state.

In the lower enclosure formed by the portion 301, there is adifferential transformer arrangement comprising three windings 309, 310and 311 as shown. These windings are substantially co-axial and mountedon a non-magnetic former 312. The upper and lower windings 309 and 311are primary windings of the transformer arrangement and are arranged tobe conencted in flux opposition with respect to each other. Winding 310is the secondary or output winding of the transformer arrangement. Thecore of the transformer arrangement is made up of a central movablemember 313 which is of sufficient length to extend through the centralwinding 310 and into the primary windings 309 and 311 as shown. Thismember is attached via a stem 314 to a threaded stud which is screwedinto the lower part of the pressure responsive member 314. The core ofthe transformer also comprises a lower pole piece 315 which isadjustable by means ofa screw adjustment 316 in the lower part of thearrangement which extends into the lower primary winding 311 and can belocked in any desired position. Also a further pole piece 317 isprovided which is integral with an outer casing 318 of magnetic materialof the transformer arrangement as shown. Air gaps are provided betweenthe pole pieces 315 and 317 to allow for movement of the centre member313 with the pressure responsive means 314.

In operation of the transducer, it is assumed that an alternating signalof sufficient frequency is applied to 309 and 31 1 so that the fluxesproduced thereby are in opposition with respect to each other and withno load on the vehicle bogie the core portion 313 is symmetricallydisposed with respect to the windings 309 and 311, the magnitude of theoutput signal derived from 310 is thus ideally zero. Movement of313towards the lower pole piece 315 of the transformer arrangement thenincreases the flux linkage of 311 with 9 and reduces that of 310 with309 and an alternating output signal is derived from 310 the magnitudeof which varies in approximately linear manner as the loading increases.

Having thus described our invention, what we claim is:

1. An electrical analogue signal-controlled, vehicle braking controlapparatus for a braking system including dynamic braking meansresponsive to an electrical command analogue signal [traction means] ina sense to increase braking with reduction of the magnitude of theanalogue signal and additional braking means, said apparatus comprisingmeans for receiving an electrical signal indicative of the degree ofdynamic braking produced by said dynamic braking means and summingmeans, including a first input for receiving the command analogue signaland a second input connected to said means for receiving said signalindicative of the degree of dynamic braking produced, for pro ducing anoutput control signal [for controlling] an increase in the magnitude ofwhich increases braking by said additional braking means so that anydeficiency in the dynamic braking dictated by said command ana loguesignal is compensated for.

2. An electrical analogue signal-controlled, vehicle braking controlapparatus comprising dynamic braking means responsive to an electricalcommand analogue signal indicative of a desired braking effort,additional braking means, and electrical control means comprising meansfor producing an electrical signal indicative of the degree of dynamicbraking produced and summing means, including a first input forreceiving said command analogue signal and second input for receivingsaid electrical signal, for producing an output control signal [forcontrolling] an increase in the magnitude of which increases braking bysaid additional braking means so that any deficiency in the dynamicbraking dictated by said command analogue signal is compensated for.

3. An electrical analogue signal-controlled, vehicle braking controlapparatus for a braking system comprising dynamic braking means andadditional braking means, said control apparatus comprising meansresponsive to an electrical command analogue signal indicative of adesired braking effort for producing avariable electrical signal inaccordance therewith, an amplifier, responsive to a vehicle weightresponsive signal and to said variable electrical signal, for producinga weight dependent electrical signal, dynamic braking control means,including adding means for adding said variable electrical signal tosaid weight dependent electrical signal, for producing a load-weightedelectrical signal for controlling said dynamic braking means, andsumming means, responsive to said command analogue signal [,1 saidweight dependent [signal] and an electrical signal indicative of thedegree of dynamic braking, [for producing] in a sense to produce anoutput control signal for controlling said additional brak-- ing meansto increase braking with a reduction in the magnitude of the outputcontrol signal so that any deficiency in the dynamic braking dictated bythe sum of the weight dependent signal and the command ana logue signalis compensated for.

4. An apparatus as claimed in claim [1] 3 wherein said variable signalcomprises a tare weight signal.

I 5. An apparatus as claimed in claim 3 wherein said electrical analoguesignal is variable over a range of values, one part of said range beingindicative of a desired braking effort and another part of said rangebeing indicative of a desired accelerating effort to be produced] 6. Anapparatus as claimed in claim 3 wherein said variable signal comprisesan A.C. signal.

7. An apparatus as claimed in claim 6 wherein said amplifier includes apressure responsive differential transformer.

8. An apparatus as claimed in claim [5] 3 wherein said analogue signalis variable over a range of values, one part of said range, ofrelatively low magnitude, being indicative of a desired braking effortand another part of said range, of relatively high magnitude, beingindicative of a desired accelerating effort to be produced by thebraking means, and said variable signal includes a parameter dependentupon the part of the range of values in which the command analoguesignal falls.

9. An apparatus as claimed in claim 8 further comprising means forproducing a reference A.C. signal, said parameter being the phase of theA.C. signal in relationship to said reference A.C. signal.

10. An apparatus as claimed in claim 9 wherein said dynamic brakingcontrol means further includes a phase sensitive rectifier circuitresponsive to the phase of said added weight dependent signal and thevariable electrical signal for producing dynamic braking in ac cordancetherewith when a predetermined phase relationship exists with respect tothe reference A.C. signal.

11. An apparatus as claimed in claim 1 wherein said summing meansincludes a magnetic amplifier having D.C. windings to which respectivesignals to be summed are applied in approximately poled D.C. form.

12. An apparatus as claimed in claim 1 further comprising a jerk controlcircuit for controlling the rate of change of the electrical commandanalogue signal.

13. An apparatus as claimed in claim 12 wherein said jerk controlcircuit comprises a constant current circuit, an output storage device,and means responsive to a non-correspondence between the output signalvoltage of the storage device and an input command analogue signal forcausing the constant current circuit to feed current to said storagedevice.

14. An apparatus as claimed in claim 13 wherein said jerk controlcircuit includes first and second constant current circuits, said firstconstant current circuit being operable, in response to an increase ofthe input signal producing such a non-correspondence between the inputsignal and the output signal voltage, to feed current in one directionto said storage device and said second constant current circuit beingoperable, in response to a decrease [an] of the input signal providingsuch a noncorrespondence between the input signal and output signalvoltage, to feed current in the other direction.

15. An electrical analogue signal controlled vehicle braking controlapparatus for a braking system having dynamic braking means andadditional braking means, the said control apparatus con'zprising anamplifier responsive to a variable electrical signal for producing avehicle weight dependent electrical signal and a magnetic amplifierresponsive to the variable electrical signal, to the vehicle weightdependent signal and to an electrical signal indicative of the degree ofdynamic braking being produced, in a sense to produce an output controlsignal for controlling said additional braking means to increase brakingwith a reduction of magnitude ofthe output control signal so that anydeficiency in the dynamic braking dictated by the sum of the weightdependent signal and the said variable electrical signal is compensatedfor by the additional braking means.

16. An electrical analogue signal-control vehicle braking controlapparatus for a braking system comprising dynamic braking means andadditional braking means, said control apparatus comprising meansresponsive to an electrical command analogue signal indicative of adesired braking effort for producing a variable a.c. electrical signalin accordance therewith, an amplifier including a pressure responsivedifferential transformer responsive to a vehicle weight responsivesignal and to said variable a.c. electrical signal for producing aweight dependent electrical signal, dynamic braking control means,including additional means for adding said variable electrical signal tosaid weight dependent electrical signal, for producing a loadweightedelectrical signal for controlling said dynamic braking means and summingmeans, responsive to said command analogue signal, said weight dependentsignal and an electrical signal indicative of the degree of dynamicbraking, for producing an output control signal for controlling saidadditional braking means so that any deficiency in the dynamic brakingdictated by the sum of the weight dependent signal and the commandanalogue signal is compensated for.

l 7. An electrical analogue signal-controlled vehicle braking controlapparatus as claimed in claim 1 6, wherein said electrical analoguesignal is variable over a range of values, one part of said range ofrelatively low magnitude being indicative of a desired braking effortand another part of said range of relatively high magnitude beingindicative of a desired accelerating effort to be effected by tractionmeans, the variable electrical signal having a phase dependent upon thepart of the range of values in which the command analogue signal fallsand the apparatus including means for producing an a.c. reference signalin relation to which said phase is determinable.

18. An apparatus as claimed in claim 17, wherein said dynamic brakingcontrol means further includes a phase sensitive rectifier circuitresponsive to the phase of said added weight dependent signal and thevariable electrical signal for producing dynamic braking in accordancetherewith when a pre-determined phase relationship exists with respectto the reference a.c. signal.

I 9. An electrical analogue signal-controlled vehicle braking controlapparatus for a braking system including dynamic braking meansresponsive to an electrical command analogue signal, and additionalbraking means, said apparatus comprising means for receiving anelectrical signal indicative of the degree of dynamic braking producedby said dynamic braking means and summing means, including a magneticamplifier having d.c. windin gs to which respective signals to be summedare applied in appropriately poled d.c. form and including a first inputfor receiving the command analogue signal and a second input forreceiving said signal indicative of the degree of dynamic brakingproduced, for producing an output control signalfor controlling saidadditional braking means so that any deficiency in the dynamic brakingdictated by said command analogue signal is compensated for.

20. An electrical analogue signal-controlled vehicle braking controlapparatus for a braking system including dynamic braking meansresponsive to an electrical command analogue signal, a jerk controlcircuit for controlling the rate of change of the electrical commandanalogue signal, and additional braking'meartsi sztitbappztrra-- tuscomprising means for receiving an electrical signal indicative of thedegree of dynamic braking produced by said dynamic braking means andsumming means including a first input for receiving the command analoguesignal and a second input connected to said means for receiving saidsignal indicative of the degree of dynamic braking produced forproducing an output control signal for controlling said additionalbraking means so that any deficiency in the dynamic braking dictated bysaid command analogue signal is compensated for.

21. An apparatus as claimed in claim 20, wherein said jerk controlcircuit comprises a constant current circuit,

- an output storage device and means responsive to a noncorrespondencebetween the output signal voltage of the storage device and an inputcommand analogue signal causing the constant current circuit to feedcurrent to said storage device.

22. An apparatus as claimed in claim 21, said jerk control circuitincluding in addition to said first mentioned constant current circuit,a second constant current circuit, said first constant current circuitbeing operable, in response to an increase of input signal producingsuch a non-correspondence between the input signal and the output signalvoltage, to feed current in one direction to said storage device andsaid second constant current circuit being operable, in response to adecrease of the input signal providing such a non-correspondence betweenthe input signal and the output signal voltage, to feed current in theother direction to the storage device.

23. An electrical analogue signal-controlled vehicle braking controlapparatus for a braking system having dynamic braking means andadditional braking means, said control apparatus comprising an amplifierincluding a pressure responsive differential transformer responsive to avariable a.c. electrical signal for producing a vehicle weight dependentelectrical signal and summing means responsive to the variableelectrical signal, to the vehicle weight dependent signal and to anelectrical signal indicative of the degree of dynamic braking beingproduced, for producing an output control signal for controlling saidadditional braking means so that any deficiency in the dynamic brakingdictated by the sum of the weight dependent signal and the said variablesignal is compensated for by the additional braking means.

24. An electrical analogue signalcontrolled vehicle braking controlapparatus as claimed in claim 23 wherein the electrical analogue signalis variable over a range of values, one part of relatively low magnitudebeing indicative of a desired braking effort and another part of saidrange of relatively high magnitude being indicative of a desiredaccelerating effort to be produced by traction means and said variablesignal having a phase dependent upon the part of the range of values inwhich the command analogue signal falls, the apparatus including meansfor producing a reference a.c. signal in relation to which said phase isdeterminable.

25. An apparatus as claimed in claim 24, wherein said dynamic brakingcontrol means furtherincludes a phase sensitive rectifier circuitrespvnsiv'e to'the phase of said added weight dependent signal and thevariable electrical signal for producing dynamic braking in accordancetherewith when a predetermined phase relationship exists with respect tothe reference a.c. signal.

26. An electrical analogue signal-controlled vehicle braking controlapparatus for a braking system having dynamic braking means andadditional braking means, the said control apparatus including a jerkcontrol circuit for controlling the rate of change of the electricalcommand analogue signal, an amplifier responsive to a vari ableelectrical signal resulting therefrom for producing a vehicle weightdependent electrical signal and summing means, responsive to thevariable electrical signal to the variable weight dependent signal andto an electrical signal indicative of the degree of dynamic brakingbeing produced, for producing an output control signal for controllingsaid additional braking means so that any deficiency in the dynamicbraking dictated by the sum of the weight dependent signal and the saidvariable electrical signal is compensated for by the additional brakingmeans.

27. An apparatus as claimed in claim 26 said jerk control circuitcomprising a constant current circuit, an output storage device, andmeans responsive to a noncorrespondence between the output signalvoltage of the storage device and an input command analogue signal forcausing the constant current circuit to feed current to said storagedevice.

28. An apparatus as claimed in claim 27, said jerk control circuitincluding in addition to the first mentioned constant current circuit, asecond constant current circuit, said first constant current circuitbeing operable, in response to an increase of the input signal producingsuch a non-correspondence between the input signal and the output signalvoltage, to feed current in one direction to said storage device andsaid second constant current circuit being operable, in response to adecrease of the input signal providing such a non-correspondence betweenthe input signal and the output signal voltage, to feed current in theother direction to said storage device.

29. An electrical analogue signal-controlled vehicle braking controlapparatus for a braking system having dynamic braking means andadditional braking means, the said control apparatus comprising anamplifier responsive to a variable electrical signal for producing avehicle weight dependent electrical signal and a magnetic amplifierresponsive to the variable electrical signal, to the vehicle weightdependent signal and to an electrical signal indicative of the degree ofdynamic braking being produced for producing an output control signalfor controlling said additional braking means so that any deficiency inthe dynamic braking dictated by the sum of the weight dependent signaland the said variable electrical signal is compensated for by theadditional braking means.

1. An electrical analogue signal-controlled, vehicle braking controlapparatus for a braking system including dynamic braking meansresponsive to an electrical command analogue signal (traction means) ina sense to increase braking with reduction of the magnitude of theanalogue signal and additional braking means, said apparatus comprisingmeans for receiving an electrical signal indicative of the degree ofdynamic braking produced by said dynamic braking means and summingmeans, including a first input for receiving the command analogue signaland a second input connected to said means for receiving said signalindicative of the degree of dynamic braking produced, for producing anoutput control signal (for controlling) an increase in the magnitude ofwhich increases braking by said additional braking means so that anydeficiency in the dynamic braking dictated by said command analoguesignal is compensated for.
 2. An electrical analogue signal-controlled,vehicle braking control apparatus comprising dynamic braking meansresponsive to an electrical command analogue signal indiCative of adesired braking effort, additional braking means, and electrical controlmeans comprising means for producing an electrical signal indicative ofthe degree of dynamic braking produced and summing means, including afirst input for receiving said command analogue signal and second inputfor receiving said electrical signal, for producing an output controlsignal (for controlling) an increase in the magnitude of which increasesbraking by said additional braking means so that any deficiency in thedynamic braking dictated by said command analogue signal is compensatedfor.
 3. An electrical analogue signal-controlled, vehicle brakingcontrol apparatus for a braking system comprising dynamic braking meansand additional braking means, said control apparatus comprising meansresponsive to an electrical command analogue signal indicative of adesired braking effort for producing a variable electrical signal inaccordance therewith, an amplifier, responsive to a vehicle weightresponsive signal and to said variable electrical signal, for producinga weight dependent electrical signal, dynamic braking control means,including adding means for adding said variable electrical signal tosaid weight dependent electrical signal, for producing a load-weightedelectrical signal for controlling said dynamic braking means, andsumming means, responsive to said command analogue signal(,) said weightdependent (signal) , and an electrical signal indicative of the degreeof dynamic braking, (for producing) in a sense to produce an outputcontrol signal for controlling said additional braking means to increasebraking with a reduction in the magnitude of the output control signalso that any deficiency in the dynamic braking dictated by the sum of theweight dependent signal and the command analogue signal is compensatedfor.
 4. An apparatus as claimed in claim (1) 3 wherein said variablesignal comprises a tare weight signal.
 6. An apparatus as claimed inclaim 3 wherein said variable signal comprises an A.C. signal.
 7. Anapparatus as claimed in claim 6 wherein said amplifier includes apressure responsive differential transformer.
 8. An apparatus as claimedin claim (5) 3 wherein said analogue signal is variable over a range ofvalues, one part of said range, of relatively low magnitude, beingindicative of a desired braking effort and another part of said range,of relatively high magnitude, being indicative of a desired acceleratingeffort to be produced by the braking means, and said variable signalincludes a parameter dependent upon the part of the range of values inwhich the command analogue signal falls.
 9. An apparatus as claimed inclaim 8 further comprising means for producing a reference A.C. signal,said parameter being the phase of the A.C. signal in relationship tosaid reference A.C. signal.
 10. An apparatus as claimed in claim 9wherein said dynamic braking control means further includes a phasesensitive rectifier circuit responsive to the phase of said added weightdependent signal and the variable electrical signal for producingdynamic braking in accordance therewith when a predetermined phaserelationship exists with respect to the reference A.C. signal.
 11. Anapparatus as claimed in claim 1 wherein said summing means includes amagnetic amplifier having D.C. windings to which respective signals tobe summed are applied in approximately poled D.C. form.
 12. An apparatusas claimed in claim 1 further comprising a jerk control circuit forcontrolling tHe rate of change of the electrical command analoguesignal.
 13. An apparatus as claimed in claim 12 wherein said jerkcontrol circuit comprises a constant current circuit, an output storagedevice, and means responsive to a non-correspondence between the outputsignal voltage of the storage device and an input command analoguesignal for causing the constant current circuit to feed current to saidstorage device.
 14. An apparatus as claimed in claim 13 wherein saidjerk control circuit includes first and second constant currentcircuits, said first constant current circuit being operable, inresponse to an increase of the input signal producing such anon-correspondence between the input signal and the output signalvoltage, to feed current in one direction to said storage device andsaid second constant current circuit being operable, in response to adecrease (an) of the input signal providing such a non-correspondencebetween the input signal and output signal voltage, to feed current inthe other direction.
 15. An electrical analogue signal controlledvehicle braking control apparatus for a braking system having dynamicbraking means and additional braking means, the said control apparatuscomprising an amplifier responsive to a variable electrical signal forproducing a vehicle weight dependent electrical signal and a magneticamplifier responsive to the variable electrical signal, to the vehicleweight dependent signal and to an electrical signal indicative of thedegree of dynamic braking being produced, in a sense to produce anoutput control signal for controlling said additional braking means toincrease braking with a reduction of magnitude of the output controlsignal so that any deficiency in the dynamic braking dictated by the sumof the weight dependent signal and the said variable electrical signalis compensated for by the additional braking means.
 16. An electricalanalogue signal-control vehicle braking control apparatus for a brakingsystem comprising dynamic braking means and additional braking means,said control apparatus comprising means responsive to an electricalcommand analogue signal indicative of a desired braking effort forproducing a variable a.c. electrical signal in accordance therewith, anamplifier including a pressure responsive differential transformerresponsive to a vehicle weight responsive signal and to said variablea.c. electrical signal for producing a weight dependent electricalsignal, dynamic braking control means, including additional means foradding said variable electrical signal to said weight dependentelectrical signal, for producing a load-weighted electrical signal forcontrolling said dynamic braking means and summing means, responsive tosaid command analogue signal, said weight dependent signal and anelectrical signal indicative of the degree of dynamic braking, forproducing an output control signal for controlling said additionalbraking means so that any deficiency in the dynamic braking dictated bythe sum of the weight dependent signal and the command analogue signalis compensated for.
 17. An electrical analogue signal-controlled vehiclebraking control apparatus as claimed in claim 16, wherein saidelectrical analogue signal is variable over a range of values, one partof said range of relatively low magnitude being indicative of a desiredbraking effort and another part of said range of relatively highmagnitude being indicative of a desired accelerating effort to beeffected by traction means, the variable electrical signal having aphase dependent upon the part of the range of values in which thecommand analogue signal falls and the apparatus including means forproducing an a.c. reference signal in relation to which said phase isdeterminable.
 18. An apparatus as claimed in claim 17, wherein saiddynamic braking control means further includes a phase sensitiverectifier circuit responsive to the phaSe of said added weight dependentsignal and the variable electrical signal for producing dynamic brakingin accordance therewith when a pre-determined phase relationship existswith respect to the reference a.c. signal.
 19. An electrical analoguesignal-controlled vehicle braking control apparatus for a braking systemincluding dynamic braking means responsive to an electrical commandanalogue signal, and additional braking means, said apparatus comprisingmeans for receiving an electrical signal indicative of the degree ofdynamic braking produced by said dynamic braking means and summingmeans, including a magnetic amplifier having d.c. windings to whichrespective signals to be summed are applied in appropriately poled d.c.form and including a first input for receiving the command analoguesignal and a second input for receiving said signal indicative of thedegree of dynamic braking produced, for producing an output controlsignal for controlling said additional braking means so that anydeficiency in the dynamic braking dictated by said command analoguesignal is compensated for.
 20. An electrical analogue signal-controlledvehicle braking control apparatus for a braking system including dynamicbraking means responsive to an electrical command analogue signal, ajerk control circuit for controlling the rate of change of theelectrical command analogue signal, and additional braking means, saidapparatus comprising means for receiving an electrical signal indicativeof the degree of dynamic braking produced by said dynamic braking meansand summing means including a first input for receiving the commandanalogue signal and a second input connected to said means for receivingsaid signal indicative of the degree of dynamic braking produced forproducing an output control signal for controlling said additionalbraking means so that any deficiency in the dynamic braking dictated bysaid command analogue signal is compensated for.
 21. An apparatus asclaimed in claim 20, wherein said jerk control circuit comprises aconstant current circuit, an output storage device and means responsiveto a non-correspondence between the output signal voltage of the storagedevice and an input command analogue signal causing the constant currentcircuit to feed current to said storage device.
 22. An apparatus asclaimed in claim 21, said jerk control circuit including in addition tosaid first mentioned constant current circuit, a second constant currentcircuit, said first constant current circuit being operable, in responseto an increase of input signal producing such a non-correspondencebetween the input signal and the output signal voltage, to feed currentin one direction to said storage device and said second constant currentcircuit being operable, in response to a decrease of the input signalproviding such a non-correspondence between the input signal and theoutput signal voltage, to feed current in the other direction to thestorage device.
 23. An electrical analogue signal-controlled vehiclebraking control apparatus for a braking system having dynamic brakingmeans and additional braking means, said control apparatus comprising anamplifier including a pressure responsive differential transformerresponsive to a variable a.c. electrical signal for producing a vehicleweight dependent electrical signal and summing means responsive to thevariable electrical signal, to the vehicle weight dependent signal andto an electrical signal indicative of the degree of dynamic brakingbeing produced, for producing an output control signal for controllingsaid additional braking means so that any deficiency in the dynamicbraking dictated by the sum of the weight dependent signal and the saidvariable signal is compensated for by the additional braking means. 24.An electrical analogue signal-controlled vehicle braking controlapparatus as claimed in claim 23 wherein the electrical analogue signalis variable over a range of values, one part of relatively low magnitudebeing indicative of a desired braking effort and another part of saidrange of relatively high magnitude being indicative of a desiredaccelerating effort to be produced by traction means and said variablesignal having a phase dependent upon the part of the range of values inwhich the command analogue signal falls, the apparatus including meansfor producing a reference a.c. signal in relation to which said phase isdeterminable.
 25. An apparatus as claimed in claim 24, wherein saiddynamic braking control means further includes a phase sensitiverectifier circuit responsive to the phase of said added weight dependentsignal and the variable electrical signal for producing dynamic brakingin accordance therewith when a predetermined phase relationship existswith respect to the reference a.c. signal.
 26. An electrical analoguesignal-controlled vehicle braking control apparatus for a braking systemhaving dynamic braking means and additional braking means, the saidcontrol apparatus including a jerk control circuit for controlling therate of change of the electrical command analogue signal, an amplifierresponsive to a variable electrical signal resulting therefrom forproducing a vehicle weight dependent electrical signal and summingmeans, responsive to the variable electrical signal to the variableweight dependent signal and to an electrical signal indicative of thedegree of dynamic braking being produced, for producing an outputcontrol signal for controlling said additional braking means so that anydeficiency in the dynamic braking dictated by the sum of the weightdependent signal and the said variable electrical signal is compensatedfor by the additional braking means.
 27. An apparatus as claimed inclaim 26 said jerk control circuit comprising a constant currentcircuit, an output storage device, and means responsive to anon-correspondence between the output signal voltage of the storagedevice and an input command analogue signal for causing the constantcurrent circuit to feed current to said storage device.
 28. An apparatusas claimed in claim 27, said jerk control circuit including in additionto the first mentioned constant current circuit, a second constantcurrent circuit, said first constant current circuit being operable, inresponse to an increase of the input signal producing such anon-correspondence between the input signal and the output signalvoltage, to feed current in one direction to said storage device andsaid second constant current circuit being operable, in response to adecrease of the input signal providing such a non-correspondence betweenthe input signal and the output signal voltage, to feed current in theother direction to said storage device.
 29. An electrical analoguesignal-controlled vehicle braking control apparatus for a braking systemhaving dynamic braking means and additional braking means, the saidcontrol apparatus comprising an amplifier responsive to a variableelectrical signal for producing a vehicle weight dependent electricalsignal and a magnetic amplifier responsive to the variable electricalsignal, to the vehicle weight dependent signal and to an electricalsignal indicative of the degree of dynamic braking being produced forproducing an output control signal for controlling said additionalbraking means so that any deficiency in the dynamic braking dictated bythe sum of the weight dependent signal and the said variable electricalsignal is compensated for by the additional braking means.